### Layout

- Use a variable width with a minimum width of 288 pixels.
- Use a variable height with a minimum height of 172 pixels.
- Center vertically and horizontally in the available space.
- Always have at least one focusable element inside a modal.
- Blocking modals (`Modeless Modal`) should be used very sparingly, only when it's critical for people to make a choice or provide information before they can proceed.
- Provide a clear way for people to dismiss the control, such as a Close button, which should always go in the upper right corner.

### Content

- Use sentence-style capitalization—only capitalize the first word. For more info, see [Capitalization](https://docs.microsoft.com/style-guide/capitalization) in the Microsoft Writing Style Guide.